Abstract
AbstractThe daily rhythm in pineal melatonin content has been characterized at 10-week intervals in male hamsters sequentially exposed to long photoperiods (14 hr light: 10 hr dark) for 10 weeks, short photoperiods (8 hr light: 16 hr dark) for 30 weeks, and then long photoperiods once again for 10 weeks. These photoperiodic manipulations induced the gonadal changes associated with the seasonal reproductive cycle experienced by this species. At the end of the initial long photoperiod, mean melatonin concentrations of 79-114 pg/gland were found throughout the day and the first 6 hr of darkness and a peak concentration of 949 pg/gland was found 8 hr after the onset of dark. Hamsters exposed to short photoperiods for either 10, 20, or 30 weeks had pineal melatonin concentrations ranging from 50 to 140 pg/gland throughout the day and the first 7 hr of darkness and peak concentrations ranging from 764 to 1025 pg/gland 13 hr after the light to dark transition. The last group of hamsters, which had been in long p...
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